BRG1 Loss Is Frequent in Lung Cancer and Transforms Lung Epithelial Cells via Transcriptional and Epigenetic Reprograming.

Background/objectives: The BRG1 loss-of-function (LOF) mutation is found in ~10% of non-small cell lung cancer (NSCLC) cases, but its role in lung tumorigenesis is unclear and so it is investigated in this study.

Methods: BRG1-knockout (KO) lines were generated from various non-malignant, pre-malignant, and malignant human lung epithelium-derived cell lines using CRISPR. The effects of BRG1-KO on cell growth, the transcriptome, the methylome, and epigenetic therapy were compared with those of wild-type (BRG1-WT) isogenic controls using standard in vitro and in vivo assays.

Results: The BRG1 protein was expressed in all non-/pre-malignant lung epithelial cells but lost in 47% (14/30) of NSCLC cell lines. BRG1-KO and cigarette smoke (CS) exposure individually transformed human bronchial epithelial cell lines (HBECs), as evidenced by anchorage-independent growth. BRG1-KO and CS produced additive to synergistic effects on sensitivity to transformation that differed across HBECs. RNA-seq analysis revealed that BRG1-KO significantly changed the expression of over 8500 genes on average, impacting lung development, function, damage repair, and cancer pathways, including axonal guidance, pulmonary wound healing, and epithelial-to-mesenchymal transition (EMT). BRG1-KO also led to the hypermethylation of >47,000 promoter CpGs within ~9500 genes on average in different HBECs, including silencing of epithelial genes involved in EMT and tumor suppressor genes. BRG1-KO also moderately increased the in vitro and in vivo sensitivity of NSCLC cells to some epigenetic drugs.

Conclusions: BRG1-LOF is frequent in NSCLC; can drive the transformation of lung epithelial cells such that they acquire properties of pre-malignant cells, indicating a potential role in lung cancer initiation; and sensitizes lung tumors to epigenetic therapy.